A hybrid vehicle may provide regenerative driveline braking to slow a vehicle. During regenerative braking, a vehicle's kinetic energy may be converted to electrical energy. The electrical energy is stored in an energy storage device where it may be held until it is needed to supply power to the vehicle or perform some other function. The energy storage device may have capacity constraints so that it may store a limited amount of electrical energy. Nevertheless, it may be desirable to continue to provide driveline braking even though the energy storage device is approaching conditions where additional charging may not be desired. However, the energy storage device may degrade if over charged.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for controlling driveline braking, comprising: providing driveline braking via an electric machine while rotation of an engine is stopped; and starting rotation of the engine in response to a battery state of charge exceeding a threshold.
By starting rotation of an engine in response to a battery state of charge, it may be possible to continue to provide driveline braking even after a battery being charged via regenerative braking is fully charged. In particular, engine rotation may be started so that the engine provides driveline braking instead of the electric machine. As a result, it may be possible to provide continuous driveline braking even as an amount of energy stored in a battery reaches a threshold level. Therefore, it may be possible to reduce use of friction braking.
The present description may provide several advantages. For example, the approach may reduce driveline torque disturbances of a hybrid driveline. Further, the approach may provide for continuous driveline braking during braking conditions. Further still, the approach may reduce friction brake degradation by reducing the use of friction braking.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.